Circulating levels of vitamin A (retinol and retinyl palmitate), the carotenoids (lutein, cryptoxanthin, lycopene, beta and gamma carotene) were studied as were two forms of vitamin E (alpha and gamma) in the serum of 7 grey gulls (Larus modestus), 7 Inca terns (Larosterna inca), and 10 Humboldt penguins (Spheniscus humboldti) housed at Brookfield Zoo.

Retinol levels were the higher in the penguins (means = 250 mcg/100ml) than the gulls (116 mcg/100ml). No retinol was present in the tern serum. However, though not analyzed specifically, there was some indication that dehydroretinol was present in tern serum. Dehydroretinol has the full biological activity of vitamin A. Thus, it is probable that the terns utilize vitamin A differently. Retinyl palmitate was present in penguin (mean = 12 mcg/100ml) and gull (mean = 11 mcg/100ml) serum. It was found in only one tern sample. Generally, the presence of circulating retinyl palmitate may be indicative of a vitamin A toxicity.

No beta nor gamma carotenoids were found. Lutein was found in all birds; gulls being the greatest (mean = 140 mcg/100ml), with terns intermediate (mean = 71 mcg/100ml), and penguins the lowest (mean = 1.9 mcg/100ml). Cryptoxanthin was present in only the gull serum. Birds have been found to deposit considerable quantities of carotenoids in various tissues including egg yolk.

Alpha-tocopherol values for gulls and penguins were similar (2694 and 2839 mcg/100ml, respectively) while the terns were higher (4732 mcg/100ml). No gamma-tocopherol was found.

The diets of the gulls and terns were identical. The penguins consumed similar diets although they had a greater selection of fish. This study showed that fish eating birds, while consuming similar diets, may assimilate dietary nutrients very differently.